17 November 2010
Earlier this week, the Japanese space agency (JAXA) announced that the sample container from the Hayabusa probe that returned to earth in June did indeed contain dust grains from the asteroid Itokawa. This makes Hayabusa the first sample return from the surface of an object beyond the moon, and is a great success for JAXA after a mission plagued with problems.
During the cruise phase, Hayabusa was hit by a solar flare, which damaged its solar panels, and then later in the cruise one of the reaction wheels failed. Reaction wheels are clever little flywheels inside spacecraft that allow the spacecraft to rotate without using rocket fuel. They work by conservation of angular momentum: if you spin the flywheel one way, the spacecraft rotates the other way to balance it out. Losing one wheel was bad enough, but when Hayabusa reached the asteroid Itokawa its second reaction wheel failed, forcing it to rely on its thrusters to point itself.
Hayabusa carried with it a small lander called Minerva, but was released incorrectly and floated off into space instead of hopping around on the surface of the asteroid. Not to be deterred, the Hayabusa spacecraft itself was sent to land on the asteroid and collect samples, but there was a loss of communications and the probe was told to abort and fly back to a safe altitude. Once communications were re-established it turned out that the probe did make it to the surface but the sampling sequence didn’t activate. Still, hoping that some dust kicked up by the landing made it into the sample container, it was sealed.
Hayabusa actually landed on Itokawa a second time, but the sampling sequence failed again, and after it ascended it developed a problem with its thrusters. That’s right, both reaction wheels died and then the thrusters started acting up! The probe was plagued with fuel leaks and communication issues all the way back to Earth but miraculously was able to re-enter the earth’s atmosphere at the correct angle for the sample container to survive and land in the Australian outback.
The capsule was recovered in June and initially it looked empty, but after carefully searching, JAXA has officially announced that there are grains in the capsule from Itokawa. Of course, a few thousand microscopic grains is a small and difficult set of samples to work with, and is disappointing compared to what could have been returned if things had gone more smoothly, but beggars can’t be choosers! Modern labs do have the technology to analyze samples this small, so despite all the difficulties, Hayabusa managed to return a viable sample of an asteroid!
Congratulations to the Hayabusa team on a successful mission against all odds!